Electric switching device comprising insulating parts comprising an acrylate resin binder

ABSTRACT

In an electrical switching device which includes insulating parts subjected to the influence of electric arcs, the insulating parts are formed of mouldings having a binder which consists essentially of a mixture of a linear acrylate polymer and a monomeric acrylate compound which is polyethylene glycol dimethacrylate or a polyethylene glycol diacrylate converted into polymerized form. The binder may contain an additive resin containing ethylenically unsaturated groups in the monomeric acrylate compound in a quantity of at most 25 percent of the total weight of linear acrylate polymer, monomeric acrylate and additive resin. The binder may also contain a powdered filler or a fibrous reinforcing material.

United States Patent [19 [111 3,786,213

Hiilmstrom g Jan. 15, 1974 ELECTRIC SWITCHING DEVICE right 1944, McGraw-Hill Book Co., Inc., page 673.

COMPRISING INSULATING PARTS Plastic Materials, by J. A. Brydson, (London 1969, COMPRISING AN ACRYLATE RESIN second edition), Pag 229. BINDER [75] Inventor: Giiran l-Iiilmstrom, Vasteras, i ry nerobert S. Macon Sweden Attorney-.lennings Bailey, Jr.

[73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden [57] ABSTRACT [22] Filed: Feb. 14, 1972 I In an electrical switching device which includes insu- [21] pp No: 226,072 lating parts sub ected to the influence of electric arcs,

the insulating parts are formed of mouldings having a binder which consists essentially of a mixture of a lin- [30] Foreign Application Priority Data ear acrylate polymer and a monomeric acrylate com- Feb. 22, 1971 Sweden 2205/71 Pound which is Polyethylene glyml dimthacrylate Jan. 19, 1972 Sweden 563/ 72 8 POlYethYlene glycol diacrylate converted P merized form. The binder may contain an additive 52 vs. Cl. 200/144 c, 200/149 A resin containing ethylenically unsaturated groups in [51 Int. Cl. H01h 33/04 the monomeric acrylate Compound in a quantity of at 58 Field of Search 200/144 0, 149 A most 25 Permt of the total Weight of linear acrylate polymer, monomeric acrylate and additive resin. The 5 References Cited binder may also contain a powdered filler or a fibrous OTHER PUBLICATIONS reinforcing material. I-lackhs Chemical Dictionary, Third Edition, copy- 8 Claims, 1 Drawing Figure ELECTRIC SWITCHING DEVICE COMPRISING INSULATING PARTS COMPRISING AN ACRYLATE RESIN BINDER BACKGROUND OF THE INVENTION l. Field of the lnvention The invention relates to an electric switching device and especially a high voltage circuit breaker in which the insulating parts are subjected to the influence of electric arcs during operation.

2. The Prior Art Insulating parts which during operation come into contact with electric arcs are subjected to high mechanical, electrical and thermal stresses. It is of decisive importance for the operation of the switching means that the material in said insulating parts is sufficiently resistant to arcs so that the material is not burnt away to too great an extent. The material must also have such properties that the influence of the arc does not give rise to polluted surfaces, primarily as a result of the formation of soot, and thus to creepage sparking. It has proved extremely difficult at the same time to achieve sufficient mechanical strength and also sufficient resistance to electric arcs. Examples of switching devices where problems of the type described arise are circuit breakers and contactors and also isolators having extinguishing chutes.

Furthermore, the requirements are permanently increasing for short breaking times for high voltage circuit breakers, i.e. that time from the moment when the breaker receives an opening impulse signal until the moment when the current is cut off. The increased requirements for short breaking times are due to the expansion of electric power transmission networks and thus the increasing short-circuit powers. In order to achieve short breaking times it is important that the voltage strength in the extinguishing chamber is built up so quickly that so-called dielectric re-ignition does not occur. The material in the insulating parts which comes into contact with the arc is therefore very important since a flash-over is often caused by creepage currents along the surfaces of the insulating parts.

Previously a great number of inorganic and organic insulating materials have been used for said insulating parts. Recently, however, moulded material with binders of synthetic resin have been used to in increasing extent, such as polyester resins and epoxy resins with powdered and fibrous fillers. In order to satisfy the requirements of mechanical and thermal strength glass fibers have been principally used as fibrous filler and reinforcing material, but even fibres of linear polymers such as polyamide and polyethylene glycolterephthalate have been used, as well as cellulose fibres. It is also known to use mouldings of acrylate resins such as polymethyl methacrylate without filler.

SUMMARY OF THE INVENTION According to the invention it has proved possible to manufacture insulating parts which have very much better resistance to electric arcs and which give a considerably shorter breaking time. The improvement is achieved by using a binder in the moulding which consists essentially of a linear acrylate polymer and a monomeric acrylate compound consisting of a polyethylene glycol diacrylate or acrylate. A likely explanation of the improvement achieved is that a binder of this type disintegrates at relatively low temperatures to produce gases which have a very favourable composition with respect to extinguishing the arc and which also have the capacity to effectively keep the arc at a distance from the surface of the insulating parts and thus save the surface from the direct influence of the arc. The mouldings also have excellent resistance to creepage current and the risk of flash-over after breaking is radically decreased.

The present invention relates more specifically to a switching device having insulating parts in the form of mouldings having a binder of an acrylate resin converted into polymerized form, which are subjected to the influence of electric arcs, characterised in that the binder consists substantially of a mixture of a linear acrylate polymer and a monomeric acrylate compound consisting of polyethylene glycol dimethacrylate and/or a polyethylene glycol diacrylate, converted into polymerised form.

As examples of suitable linear acrylate polymer may be mentioned a polymer of methylmethacrylate, methylacrylate, ethyl methacrylate or ethyl acrylate or a copolymer of two or more of these substances.

As examples of polyethylene glycol dimethacrylates and polyethylene glycol diacrylates may be mentioned dimethacrylates and diacrylates of diethylene glycol, triethyleneglycol, tetraethylene glycol, pentaethylene glycol, heptaethylene glycol and septaethylene glycol.

The content of linear acrylate polymer is preferably l0 40 per cent and the content of polyethylene glycol dimethacrylate and/or polyethylene glycol diacrylate 90 per cent of the total weight of these substances.

The acrylate polymer and the monomeric acrylate compound may to a limited extent be provided with an additive resin containing ethylenically unsaturated groups which are polymerisable with the unsaturated groups in the monomeric acrylate compound. As examples of such additive resins may be mentioned unsaturated polyester resins, partially polymerised allyl esters, for example diallylphthalate and diallylmaleate, acrylmodified, preferably cycloaliphatic epoxy resins and unsaturated polybutadieneresins, for example having a molecular weight of 1,000 3,000 and containing approximately percent of the unsaturated groups in l,2-position. The quantity of additive resin should be at the most 25 i.e. O 25 of the total weight of acrylate polymer, polyethylene glycol dimethacrylate or polyethylene glycol diacrylate and additive resin, i.e. of the weight of the binder.

The unsaturated polyester resin may be of conventional type. It can be produced in the normal manner by esterifying ethylenically unsaturatedand saturated, preferably aliphatic dicarboxylic acids or corresponding anhydrides with an equivalent quantity or aslight excess of bifunctional alcohol. As examples of unsaturated acids which can be used for this purpose may be mentioned maleic acid, fumaric acid, itaconic acid as such, or in the form of anhydrides. Examples of saturated acids which can be used are primarily adipic acid, sebacic acid, succinic acid as such or in the form of anhydrides. As examples of suitable bifunctional alcohols may be mentioned glycols such as ethylene glycol, propylene glycol and butylene glycol as well as polyglycols such as diethylene glycol, triethylene glycol and dipropylene glycol.

The mouldings may also contain inorganic and organic powdered filler, such as chalk, kaolin, dolomite, bauxite, mica powder, silica powder, zirconium dioxide, zirconium silicate, silicon carbide, aluminium trihydrate, cellulose powder, polyacetal powder (polyoxymethylene), etc. The quantity of powdered filler may be at the most 70 suitably l 70, and preferably 15 60 per cent of the weight of the moulding, i.e. the total weight of the binder, fibrous material and powdered filler. The mouldings may also contain fibrous reinforcing material such as fibres of polyvinyl alcohol, fibres of acetalised polyvinyl alcohol polyethylene glycol terephthalate fibre, polyamide fibre, polyacrylonitrile fibre, regenerated cellulose fibre, cotton fibre, sisal fibre, alkali-free silica fibre, alkali-free asbestos fibre and alkali-free glass fibre. The length of the fibres in moulding compounds is suitably l 100 mm, preferably 3 50 mm and for injection moulding compounds suitably l 50 mm, preferably 1 10 mm. Their diameter is suitably l 50 microns. The quantity of fibrous reinforcing material is at the most 60, suitably l 60 and preferably 25 percent, of the weight of the moulding. Certain of the fibre materials mentioned, such as glass and asbestos, should be used in small quantities in order to avoid problems with reduced insulating ability when the insulating part is subjected to heating from the arc. Such fibrous materials should therefore be used together with other fibrous materials if the percentage of fibrous material is to be high.

Briefly, when a binder according to the present invention is used in an insulating part the advantages previously stated are gained over an insulating part which, part from the binder, is identical to the insulating part in question, i.e. it is constructed of the same constituents otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further explained by describing a number of embodiments by way of example with reference to the accompanying drawing which shows schematically a high voltage circuit breaker of minimum liquid type with transverse extinguishing chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit breaker shown has a cylindrical extinguishing chamber 1 and a cylinder 2 concentric with this chamber, both of glass-fibre reinforced plastic. At the upper end of these parts is a metallic cover 3 provided with a current terminal 4 connected to the stationary contact 5 of the circuit breaker. The movable contact 6 of the braker consists of a contact plug which can be displaced within the current collector 7 and through an arcing chamber 8 in relation to the stationary contact 5 arranged in the upper part of the arcing chamber. A number of extinguishing chamber plates 9 are arranged horizontally in the arching chamber. The lower surface of each plate is flat over the entire area of the plate. Each plate has a central hole 12 for the movable contact and a substantially radial groove at the top which extends from the hole 12 to an exhaust channel 11 inside the wall of the extinguishing chamber. Said groove thus forms a horizontal gap (transverse blowing gap) which leads from the arcing chamber 8 and opens out into the exhaust channel 11. The thickness of the material of each plate is greater towards the exhaust channel 11, i.e. in those parts which surround and are higher than the radial groove than towards the opposite end from the hole 12, so that there are open spaces between the plates towards the latter direction, as can be seen from the drawing. The plates are stacked on each other, in close contact with each other where the thickness of the plates is greatest (behind the plane shown in the drawing). In order to protect the inner wall of the extinguishing chamber against the hot gases blown out through the gaps 10, a cylindrical screen 17 of moulded material reinforced with, for example, polyvinyl alcohol fibres may be arranged inside the cylinder 1 along a part of its circumference. The binder in this material may be for example of the same sort as that mentioned for the insulating parts subjected to the influence of electric arcs, as for the plates 9. The inner wall of the extinguishing chamber cylinder 1 may also be protected by giving the plates 9 of the extinguishing chamber the same diameter as the inner diameter of the extinguishing chamber cylinder and shaping each plate with a hole running in the axial direction spaced from the periphery and thus from the wall of the extinguishing chamber. The holes in the plates stacked on top of each other thus together form an exhaust channel corresponding to the exhaust channel II in the drawing.

The circuit breaker is filled with liquid, for example oil, to the level 13 in the cover. A porcelain insulator 14 is arranged around the cylinder 2. During a breaking process the oil in the arc zone is vaporized due to the influence of the are and an extremely high pressure is thus built up in the arcing chamber 8. As the transverse blasting gaps 10 are exposed by the movable contact 6, the arc is subjected to a powerful flow of oil and gas which cools and deionises the are. In order to ensure that small currents are broken, a number of liquid pockets 15 may be arranged in the lower part of the extinguishing chamber.

In the arrangement shown the extinguishing chamber plates 9 are subjected to the influence of an arc. According to the present invention these plates consist of a moulding with a binder substantially comprising a mixture of a linear acrylate polymer and a monomeric acrylate compound consisting of polyethylene glycol dimethacrylate or polyethylene glycol diacrylate or a mixture of these monomeric compounds, converted into polymerised form. The following are some examples of how the plates are manufactured.

EXAMPLE I moulding compound is manufactured of the following components:

30 parts by weight of a resin consisting of per cent by weight tetraethylene glycol dimethacrylate and 25 per cent by weight polymethylmethacrylate having a molecular weight of 140,000

0.3 parts by weight tert. butylperbenzoate IO parts by weight polyethylene glycol terephthalate fibre in the form of staple fibre having a length of 6 mm 45 parts by weight kaolin 1 part by weight zinc stearate The ingredients are kneaded together in a sigma kneader to a homogenous pulp similar to cotton waste. Mouldings are produced by compression moulding at C using a pressure of I00 kg/em for 4 minutes.

EXAMPLE 2 30 parts by weight of a resin containing 60 per cent by weight triethylene glycol diacrylate and 20 per cent by weight of a copolymerisate of equal parts by weight methylmethacrylate and ethyl acrylate having a molecular weight of 130,000 and 20 per cent by weight polybutadiene resin having a molecular weight of 1,000 containing approximately 85 percent of the unsaturated groups in 1,2-position and the rest mainly in 1,4- trains. (from Hystl Development Co., USA) 0.5 parts by weight butyl perbenzoate 15 parts by weight polyamide fibre 6 in the form of staple fibre having a length of 12 mm 40 parts by weight silica 2 parts by weight zinc stearate The moulding compound is manufactured and moulded in the same way as the compound described in Example 1.

EXAMPLE 3 A moulding compound is manufactured of the following components:

30 parts by weight of an acrylate resin consisting of 75 parts by weight triethylene glycol dimethacrylate and 25 per cent by weight polymerised methyl methacrylate having a molecular weight of 140,000

0.5 parts by weight butyl perbenzoate 20 parts by weight cellulose powder 1.5 parts by weight zinc stearate 48 parts by weight kaolin The moulding compound is manufactured and moulded in the same way as the compound described in Example 1.

EXAMPLE 4 30 parts by weight of a resin consisting of 60 per cent by weight polyethylene glycol dimethacrylate of equal parts by weight tri-, tetra-, pentaand hexaethylene glycol dimethacrylate, 25 per cent by weight polymethyl methacrylate having a molecular weight of about 140,000 and 15 per cent by weight of a prepolymerised diallylphthalate resin (Dapan R from FMC) 0.4 parts by weight benzoyl peroxide parts by weight acrylonitrile fibre in the form of staple fibre having a length of mm 70 parts by weight zirconium silicate 1 part by weight zinc stearate The moulding compound is manufactured and moulded in the same way as the compound described in Example 1.

EXAMPLE 5 30 parts by weight of a resin consisting of 75 per cent by weight triethylene glycol diacrylate and 25 per cent by weight polymethylmethacrylate having a molecular weight of 140,000

0.5 parts by weight benzoyl peroxide 30 parts by weight cellulose fibre having a length of 3 mm 2 parts by weight zinc stearate The moulding compound is manufactured and moulded in the same way as the compound described in Example 1.

EXAMPLE 6 A moulding compound is manufactured and moulded in the same ways as that described in Example 4 with the exception that the diallylphthalate resin is replaced by an equal quantity of an unsaturated polyester resin produced in conventional manner from diethylene glycol and maleic acid in the proportions 1.1 mol diethylene glycol per mole maleic acid by boiling at C to an acid number of 40.

EXAMPLE 7 A moulding compound is manufactured and moulded in the manner described in Example 1 with the exception that one fourth of the polyethylene glycolterephthalate fibre is replaced by alkali-free asbestos fibre.

EXAMPLE 8 A casting compound is manufactured from the following components:

60 parts by weight tetraethylene glycol dimethacrylate 38 parts by weight of a copolymerisate of equal parts methylmethacrylate and ethyl acrylate 1 part by weight benzoyl peroxide.

The linear acrylate polymer is dissolved in the tetraethylene glycol dimethacrylate at 50 C. The solution obtained is used to cast mouldings. Curing is performed at 70 C for 1 hour.

The compounds described in Examples 1 8 can be i used not only for manufacturing extinguishing chamber plates in high voltage circuit breakers, but also for manufacturing other insulating parts which are subjected to the influence of electric arcs in switching devices of different types, such as extinguishing chutes in contactors and isolators.

1 claim:

1. Electric switching device having at least one insulating part in the form of a moulding having a binder of an acrylate resin converted into polymerized form, which is subjected to the influence of electric arcs, in which the binder consists essentially of a mixture of a linear acrylate polymer and a monomeric acrylate compound from the group consisting of polyethylene glycol dimethacrylate and a polyethylene glycol diacrylate, converted into polymerised form.

2. Electric switching device according to claim 1, comprising a high voltage circuit breaker comprising an extinguishing chamber, in which the insulating part constitutes an extinguishing chamber plate in the extinguishing chamber.

3. Electric switching device according to claim 1, in which the binder contains an additive resin containing ethylenically unsaturated groups which are polymerisable with the unsaturated groups in the monomeric acrylate compound, the weight of the additive resin constituting at the most 25 per cent of the total weight of linear acrylate polymer, monomeric acrylate compound and additive resin.

4. Electric switching device according to claim 1, in which the linear acrylate polymer consists essentially of a polymer of at least one member from the group methyl methacrylate, methyl acrylate, ethyl methacrylate and ethyl acrylate.

5. Electric switching device according to claim 1, in which the monomeric acrylate compound consists essentially of a dimethacrylate or diethacrylate of a memwhich the moulding contains a powdered filler in a quantity of at the most per cent of the weight of the moulding.

8. Electric switching device according to claim 1, in which the moulding contains a fibrous reinforcing material in a quantity of at the most 60 per cent of the weight of the moulding.

Patent .0

f UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated Januery 15, 1974 I fi j Goren Holmstrom' It is certified that error appears in the abbve-identified patent and that said Letters Patent are hereby eorre'cted as shown below:

insert a Signed an s eeled this 18th day'of' June 197M;

(SEAL) Atteatz,

EDWARD M.FLE'1CHER,JR. r c, msrmnunmn I Atteating Officer Commissioner of Patents Patent No. 35 3 Dated UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION January 15, 1974 Inventofls) Goran Holmstrom It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

sigma an sealed this 18th day of June 197 p:

( mm Attest:

EDWARD umwrclmmm. a c. MARSHALL-own a a a H Attesting Officer Commissioner offatenta 

2. Electric switching device according to claim 1, comprising a high voltage circuit breaker comprising an extinguishing chamber, in which the insulating part constitutes an extinguishing chamber plate in the extinguishing chamber.
 3. Electric switching device according to claim 1, in which the binder contains an additive resin containing ethylenically Unsaturated groups which are polymerisable with the unsaturated groups in the monomeric acrylate compound, the weight of the additive resin constituting at the most 25 per cent of the total weight of linear acrylate polymer, monomeric acrylate compound and additive resin.
 4. Electric switching device according to claim 1, in which the linear acrylate polymer consists essentially of a polymer of at least one member from the group methyl methacrylate, methyl acrylate, ethyl methacrylate and ethyl acrylate.
 5. Electric switching device according to claim 1, in which the monomeric acrylate compound consists essentially of a dimethacrylate or diethacrylate of a member from the group diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol and heptaethylene glycol.
 6. Electric switching device according to claim 1, in which the quantity of linear acrylate polymer is 10 - 40 per cent and the quantity of monomeric acrylate compound 60 - 90 per cent of the total weight of these substances.
 7. Electric switching device according to claim 1, in which the moulding contains a powdered filler in a quantity of at the most 70 per cent of the weight of the moulding.
 8. Electric switching device according to claim 1, in which the moulding contains a fibrous reinforcing material in a quantity of at the most 60 per cent of the weight of the moulding. 